In recent years, digital data reproducing apparatuses such as portable music players which employ flash memories and utilize the high compression techniques for digital data have appeared in the market. An example of such an apparatus is the MP3 player which handles music data and utilizes MP3 (MPEG3) technology. Because of the use of the high compression technique, the amount of digital data to be stored in the flash memory is reduced considerably. As a result, reproduction of, for example, music, for a longer time is possible even if the memory capacity is less. Moreover, such digital data reproducing apparatuses are excellent in portability, they consume less power, and are lightweight.
The digital data, e.g., music data reproduced by such a digital data reproducing apparatus is a copyright product. However, since the digital data or music data is small in data capacity, it can be transferred in a short time and can be easily carried by a user while storing the data in a small-sized recording medium such as a flash memory. As a result, the problem which the digital data or music data is illegally distributed and used disadvantageously occurs.
To deal with this problem, various measures have been now proposed to prevent the illegal distribution and the illegal use of copyright digital data. A portable music player which employs a flash memory, for example, is configured to use a flash memory card which has a copyright protection function in advance and, therefore, protects the copyright of digital data by using an authentication system between the flash memory card and the music player. The method of this type has a disadvantage in that the usage conditions of the operating system (OS) of a personal computer which a user uses are given large restrictions.
If the copyright protection method is applied to a digital data reproducing apparatus, such as a portable music player, which reproduces digital data using a flash memory card, the electrical circuit mounted configuration of this portable music player has to be changed, with the result that the development cost thereof is disadvantageously pushed up.